1. Field of the Invention
The present invention relates to a method for manufacturing a quartz piece, especially relating to a technology to obtain the quartz piece by forming an end surface of the quartz piece perpendicularly to its front and back surfaces so as to reduce the deterioration of the CI and the temperature characteristic failure.
2. Description of the Related Art
A quartz resonator is, for instance, a device which includes a quartz piece (quartz blank) and a pair of electrodes for excitation (excitation electrodes) installed on both front and back surfaces of the quartz piece, and has been widely used in electronic parts such as an oscillator or the like as a reference source for frequencies and time by utilizing the specific character in which once voltage is applied on the excitation electrodes, crystal oscillation is excited by piezoelectric opposite effect of the quartz.
As the manufacturing process of a conventional quartz resonator, a large number of quartz pieces of a prescribed shape such as the shape of a strip of paper (rectangular) are first cut off from a wafer composed of, quartz crystal for instance, and the respective cut-off quartz pieces are etched for the purpose of obtaining desired frequency characteristics so that the thickness thereof is adjusted. After the etching, the quartz piece is cleaned and the excitation electrodes are formed on both surfaces thereof, and a pair of derivation electrodes which are electrically connected to the respective excitation electrodes are formed, for instance, in a way such that they are spread across from the front surface to the back surface of the quartz piece through the end surface. The quartz piece in which the respective electrodes are thus formed and composed as a quartz resonator, is enclosed in a package, for instance, and the derivation electrodes are electrically connected to electrodes arranged in the package, and then it is shipped as a product.
In recent years however, since the miniaturization of a quartz piece has become more advanced, it has become difficult to mold a pallet for carrying out the etching processing in accordance with the size of a quartz piece and the pallet for performing cleaning processes, which makes it difficult to conduct the etching processing and cleaning processing uniformly within the plane of the quartz piece.
Because of the reason described above, it is attempted that a wafer W is formed by etching so that the forming area for the quartz piece has a prescribed thickness, then etching is conducted along the periphery of the quartz piece forming area in a manner that a connecting portion between the quartz piece and the wafer is left, and a groove (through hole) drilled through the front surface to the back surface of the wafer is formed to form the outside shape of the quartz piece. Then, after cleaning it in a state that the quartz piece is fixed on the wafer by the above-described connecting portion, electrodes spread across the front surface to the back surface of the quartz piece as described above are formed utilizing the groove (through hole), and then, the quartz piece is cut off from the wafer.
The wafer W at the time of forming the outside shape of the quartz piece as described above will be explained using FIG. 9. The wafer W is composed of an AT cut quartz, and metal films 12 which serve as a mask for etching a quartz layer 11 are deposited on both front and back surfaces of the quartz layer 11. A mask pattern 12a in a square-frame shape is opened along the quartz piece forming area to form, for instance, the outside shape of the rectangular quartz piece in each metal film 12 so that the quartz layer 11 is exposed. Note that a resist film 13 which is deposited for forming the mask pattern 12a is arranged on the upper portions of the respective metal films 12. Although only one of the mask patterns 12a is shown in the drawing, a large number of the mask patterns 12a are actually formed, for instance, at intervals over the whole device forming area 14 which is the area surrounded by a chain line. The arrow Z′ in the drawing indicates the axis slanting at a prescribed angle from the Z axis which is a crystal axis of the quartz, the arrow X indicates the X axis which is a crystal axis respectively, and the mask pattern 12a is formed along these axes.
As the quartz that composes the wafer W, the previously described AT cut quartz is mainly used because it has a merit of obtaining favorable frequency stability or the like when the quartz resonator is used at around a room temperature. The AT cut quartz has, however, anisotropy which is responsible for the cause of the following problem during etching to form the outside shape of the quartz piece.
FIG. 10 shows how the wafer W which is an AT cut quartz substrate is immersed in a solution containing such as hydrofluoric acid, and the vertical cross sectional face shown by the arrow in a chain line in FIG. 10 is etched along the pattern 12a. As for the Z′ axis, if the right side of the wafer W seen from the front side in the drawing is called +Z direction, and the left side is called −Z direction, the rate of etching in the −Z direction is greater compared with the rate of etching in the +Z direction in the etching which advances from the front side of the wafer W toward the back side as shown in FIG. 10A to FIG. 10C. Accordingly, the wafer W is etched obliquely from the +Z direction to the −Z direction. In the etching which advances from the back surface side of the wafer W toward the front side, the rate of etching in the +Z direction is greater than the rate of etching in the −Z direction, so that the wafer W is etched obliquely from the −Z direction to the +Z direction. As a result, after the etching is completed, protrusions 15 are left on the end surface along the X direction of the quartz piece as shown in FIG. 10D.
FIGS. 11A to 11C show an enlarged quartz layer 11 in the mask pattern 12a during etching. The reason why the etching advances in a manner as described above is because the direction of crystal arrangement in the quartz layer 11 advances obliquely as shown in these drawings, and the etching progresses along the direction of the crystal arrangement.
It is preferable for the end surface of a small quartz piece having a high frequency to be formed perpendicularly to the front and back surfaces thereof, and if the protrusions 15 are formed on the end surface as described above, it might cause the deterioration of the CI (crystal impedance) and the temperature characteristic failure of the quartz piece. In addition, when the above-described derivation electrode is formed by forming a metal film is formed on the quartz piece 13 by means of, for instance, sputtering after forming the outside shape of the quartz piece by conducting etching as described above, since the surface area of the end surface of the quartz piece becomes larger than an expected area due to the protrusions 15, the thickness of the metal film formed on the end surface is smaller than an expected thickness, which makes the electric resistance of the metal film higher than expected. As a result, the CI value (equivalent resistance value) of the quartz resonator might be high (deteriorate) and the oscillation loss could be large.
In Patent Documents 1 and 2, the technology of conducting etching to get a smooth quartz surface while reducing the effect of the quartz anisotropy is described, but the end surface of a quartz piece is paid no attention as described above, and the inventions described in the above documents cannot solve the above-described problems.
[Patent Document 1]
Japanese Patent Application Laid-open No. Hei 8-242134 (column 0017, column 0020)
[Patent Document 2]
Japanese Patent Application Laid-open No. 2005-64582 (column 0033, column 0034)